Large-sized umbrellas, such as beach umbrella and garden umbrella, are well known. A conventional large-sized umbrella is shown in FIG. 1 of the attached drawings, comprising a shank 10 having a crown 11 fixed to a top end thereof. A runner 12 is fit over and axially movable along the shank 10. A plurality of rib-stretcher sets 13 are connected between the crown 11 and the runner 12 for supporting a canopy (not shown) of the umbrella. The shank 10 is separated into an upper and lower sections between which a joint 15 is formed for allowing the upper section to rotate with respect to the lower section in order to change the direction of the umbrella canopy as shown in FIG. 2 for tracking the sun.
A rope-winding device 14 is fixed to the lower section of the shank 10 proximate a lower end thereof winding/unwinding a rope 16. The rope 16 is partially received in an axially-extending central bore (not shown) of the shank 10. The rope 16 extends from the rope-winding device 14, through the joint 15 and a roller or pulley (not shown) rotatably fixed to the shank 10 proximate the crown 11, and is connected to the runner 12 whereby by actuating the rope-winding device 14 by means of a crank arm 17 to wind/unwind the rope 16 onto/from the rope-winding device 14, the runner 12 is moved toward/away from the crown 11 for opening/closing the umbrella.
Such a conventional umbrella opening mechanism, however, has disadvantages. For example, since the runner 12 is driven by a single rope 16 that is attached to the runner 12 at one side thereof thereby leading to a force unbalanced condition which causes a frictional engagement between one side of the runner 12 and the shank 10. A smooth movement of the runner 12 is thus prohibited.
Attaching two ropes to two opposite sides of the runner is an idea solution for the force-unbalancing problem. However, since the joint 15 which provides only a very limited space for the two ropes to simultaneously extend therethrough, it is not possible to connect two ropes between the runner 12 and the rope-winding device 14.
It is thus desirable to have an umbrella opening mechanism that overcomes the problems encountered in the prior art designs of the large-sized umbrellas.